Well he would have been protected and gone through procedures to avoid such an outcome. So the logical theory is that he fucked someone over there. Maybe he met a girl and was bowled over ebolaed over
The jokes go downhill from here....
Seriously though, the only way a new disease like Ebola could get such a large grip so fast is to appear in a country like that (avoiding major media attention for long enough) and then shifting over. Its a media savvy disease.